Wednesday, April 3, 2013

How to clean a WHO Dunnit slot reel motor

The stepper motors that drive the slot machine reels on a WHO Dunnit pinball machine eventually need cleaning. Here's how I dunnit, illustrated.

Yes, we have been doing an awful lot of maintenance lately on our pinball machines. It seemed like once we finally got the board replaced for our new WHO Dunnit, another problem came up. In this case, one night I noticed that the left-most slot machine reel wasn't matching what the DMD was displaying when it would turn. By the next morning, it had stopped altogether.

I went online to research the problem (thanks, Google). This is a common problem with these motors, and in most cases, it turns out, the motor has just become jammed up with metal shavings. The motors themselves are pretty hearty, so it's less common that they have actually burned out. That was good news, because you simply can't buy this particular motor anymore. I found a German company, Kollmorgen, that used to sell them (USED TO), a company that repairs these motors, and also mention that certain pinball suppliers had them in stock... in 2009. And even at that time the fact was noteworthy. I emailed Kollmorgen just in case they still had them, but at the time of this writing, have not heard back. So my step 1 option was to try and clean our existing motor.

WHO Dunnit slot reel housing

It's not easy getting at these motors. All three are in a large metal housing under the playfield, held in place with 8 screws. Each slot reel/motor set is in its own metal housing. The motor has two circuit connectors, and the top one must be removed to remove the motor housing. What went through my head at this point was, "I'm so glad it was one of the outer reels that stopped turning and not the middle one!" The plastic reel is held in place by a set screw, and that's easy to remove.

The reel connected to the motor by a set screw

I also want to take a moment to mention, I am not the go-to pinball tech in our house. That's my husband, but he was pretty fed up with the machine at this point after the board issues, and I wanted to step up to the plate and try to fix this motor myself. It is by far the most ambitious maintenance I've attempted to date. I'm usually the one cleaning the glass. :) He was also at work on this day, and I didn't tell him I was attempting this.

motor housing

So anyway, after carefully disassembling things down to where I could actually get at the motor, I was able to remove it, and then take off one side of the casing. I was at a loss for a while as to what needed cleaning, or what to do from there, and this is one reason I wrote this article. You can find lots of mentions of cleaning these stepper motors (it's evidently the same motor used in Scared Stiff, by the way), but no pictures on what exactly that entails. Eventually I realized that pushing on the inner gear assembly just sort of slid that part out. Once I got that out, it was pretty evident that it did indeed need a cleaning. I took it upstairs to MY laboratory... the kitchen.

note shavings between the two gears - yuck!

The amount of powder and metal shavings along the inner edge was impressive. Now the pain in the BUTT with cleaning this is, the shaft housing is pretty freaking magnetic. The shavings, of course, are extremely attracted to it. Like they have found their one true love and they are never letting go. I used broken toothpicks to get in there, but it took some time. Once, I put the motor too close to the paper towel where I was keeping the shavings, and BOOM, they jumped right back on. ARGH!!

metal shavings removed

Once I had removed all the shavings I could, also going in with the edge of a paper towel to really just clean this as much as possible, I went back downstairs, gave both that and the housing a thorough attack with a can of compressed air, and put the motor back together. Before putting everything back in place, I turned on the machine, and held my breath. The moment the power came on I felt the motor twitch, and my hopes lifted. Sure enough, when the pin went through its reel spin on startup, the formerly defunct wheel spun like a champ. Victory! It was fully as great a feeling as getting a high score.

I considered taking out the other two motors then and giving them a cleaning; they are probably going to do the same thing eventually. But in pinball, it is best to heed the old adage, "if it aint broke, DON'T FIX IT." I read a thread on pinside once from a guy who wanted to clean the T-Rex on his Jurassic Park. It was working fine, he just wanted to clean it. Everyone warned him not to. He did it anyway, and sure enough, after reassembling the T-Rex, it didn't work properly. I'm sure he got it going again eventually, but the point is, don't go out of your way to find headaches in a pinball machine; they will come to you.